This application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2006-318764 filed in Japan on Nov. 27, 2006, the entire contents of which are hereby incorporated by reference.
The present invention relates to roller drive control methods of fixing apparatuses in electrophotographic image forming apparatuses.
These image forming apparatuses are provided with fixing apparatuses that melt and firmly fix unfixed toner onto a recording paper. In this type of fixing apparatus, a thermal fixing roller system is often used in which, while the recording paper is sandwiched and transported in a pressing area (nip region) between a heat roller and a pressure roller, the recording paper is subjected to heat and pressure by the heat roller and the pressure roller so that toner on the recording paper is thermally melted and fixed there.
In these thermal fixing roller system fixing apparatuses, the peripheral rotation velocity of the heat roller is generally controlled at a velocity of 1.005 to 1.03 times the print processing speed of the image forming apparatus. This velocity is a velocity for keeping the recording paper that enters the pressing area from being detained in the pressing area and is a velocity for eliminating the delay of nipping when the leading edge of the recording paper that is entering impacts against the pressing area.
On the other hand, not all the toner that is melted in the pressing area becomes firmly fixed onto the paper after passing through the pressing area, and a portion thereof is rotated while adhering to the heat roller, which then smears surfaces of components such as a separation claw for the recording paper that is in contact with the heat roller, a detection sensor for detecting a surface temperature of the heat roller, and the pressure roller. To eliminate such smearing in conventional fixing apparatuses, a cleaning unit for cleaning toner that has adhered to the surface of the heat roller is arranged downstream from the pressing area on an outer circumferential surface of the heat roller and downstream from the separation claw. The cleaning unit is provided with a cleaning member, such as a web sheet for example, that presses against the heat roller with a predetermined pressure and carries out collection of toner that adheres to the web sheet and cleaning of the heat roller.
However, as mentioned above, the separation claw is arranged on a downstream side of the pressing area and on an upstream side of the cleaning unit, and therefore under existing circumstances it is not possible to clean the toner that adheres to the separation claw.
Ordinarily, when the print processing speed is slow, the number of sheets processed per hour is small and the amount of toner that adheres to the separation claw is also small. Thus, when the toner that is in a melted state adhering onto the separation claw is moved in reverse to the heat roller and is transported, the cleaning capability of the cleaning member (web sheet) of the cleaning unit is sufficient to enable cleaning of the toner that has been subjected to reverse movement.
However, the print processing speeds of image forming apparatuses have increased in recent years, and conventional speeds of approximately 300 to 400 mm/sec have now become 500 to 700 mm/sec, thereby achieving high speed processing in which the number of sheets processed per unit of time is from 100 to 120 sheets per minute. Along with this, image forming apparatuses have also become more multifunctional, and developments in color print processing have also advanced as a part of this. For this reason, there has been a tendency for the amount of toner that adheres to the heat roller to increase from year to year and along with this the amount of toner that adheres to the separation claw is also increasing. And when the amount of toner that adheres to the separation claw increases, the amount of toner that re-adheres to the heat roller after the above-mentioned reverse movement also increases, and therefore the cleaning capability of the web sheet, which is the cleaning member of the cleaning unit, is undesirably exceeded, and this poor cleaning becomes a cause of smearing of other components (such as the detection sensor that detects the surface temperature of the heat roller as well as the pressure roller).
In order to address this problem, in JP H10-307503A, instead of a cleaning member such as a rubber blade or a felt cloth that are used in conventional fixing apparatuses, a web cleaning apparatus is disclosed in which a continually new cleaning region can be selected and, moreover, the contact surface area on the heat roller can also be set as desired.
In the web cleaning apparatus described in JP H10-307503A, the contact region between the heat roller and the cleaning web (web sheet) of the cleaning member is fixed, and also the web sheet itself is thin (ordinarily a cloth having a thickness of several tens to 150 μm is used) and therefore increases in the pressing force at the contact region cannot be expected. For this reason, there is a problem in that when a large amount of toner subjected to reverse movement from the separation claw to the heat roller as described above is transported in, there is a possibility of an occurrence of adhered toner escaping through the pressing area (nip region) at the heat roller.